A wireless communication system typically includes a communication network providing coverage of a designated geographic region and a plurality of subscriber units. The wireless communication system generally enables a subscriber unit to communicate with other communication devices, such as for example, other subscriber units, the Internet and traditional phones, via the communication network. Communication between subscriber units and the communication network typically occur over radio frequency (RF) channels that provide physical paths over which communication signals such as voice, data and video are transmitted.
The communication network includes a plurality of base transceiver stations (BTS) which provide communication coverage of a specific geographic area. The area covered by the communication network is typically divided into a number of smaller communication sites (cells) where each communication site is serviced by at least one BTS. Each BTS includes at least one radio transceiver for enabling communication with one or more subscriber units operating within the associated cell. The BTSs are coupled to at least one base station controller (BSC). Depending on the configuration of the communication network, a BSC may be adapted to control a single BTS or a cluster of multiple BTSs. Each BSC is further interfaced to a mobile switching center (MSC). The MSC communicatively couples the BSC to a public switched telephone network (PSTN) and potentially to other communication networks.
Each BTS is generally associated with a BTS controller for managing the cell resources for that BTS. In many communication systems, the BTS controller is integrated with the BSC such that the resource allocation functions are performed by the BSC, while in other systems, such as the Integrated Digital Enhanced Network System (iDEN), each BTS includes a BTS controller for managing its own resources.
Each communication site is typically assigned a dedicated control channel and a number of traffic channels for handling call traffic within the communication site. The control channel, typically under the control of the BTS controller, is utilized by the BTS and subscriber units to request and establish communication service. The control channels typically continuously broadcast system data and a listing of neighboring BTSs.
In order to initiate or receive calls, a subscriber unit must first register with the communication network. The subscriber unit begins by monitoring the strength of the control signals transmitted via control channels by different BTSs within range of the subscriber unit. The subscriber unit then registers with the communication network via the control channel for one of the BTSs, typically the BTS transmitting the control signal having the greatest signal strength. The subscriber unit also stores the listing of neighboring communication sites associated with the selected BTS in a subscriber unit memory.
Once the registration process is complete, the subscriber unit is enabled to initiate and receive calls via the selected BTS. To initiate a voice call, such as for example an interconnect call or a dispatch call, or a data packet transfer, such as for example downloading e-mail, the subscriber unit issues a message to the selected BTS via the control channel. The BTS controller then determines whether the subscriber unit is attempting to initiate a voice call or a data packet transfer. If the BTS controller determines that the subscriber unit is attempting to initiate a voice call, the BTS controller dynamically assigns a traffic channel to the subscriber unit and communicative coupling is established between the subscriber unit and the selected BTS. If the subscriber unit is attempting to initiate a data packet transfer, the BTS controller allocates unused traffic channels for data packet transmission to the subscriber unit thereby establishing communicative coupling between the subscriber unit and the selected BTS. A predefined number of traffic channels are typically reserved for voice calls so that data packet transmissions do not impact the BTS's ability to accommodate voice calls. The BTS controller continuously monitors the availability of traffic channels and dynamically reassigns traffic channels as necessary to support both voice calls and data packet transmissions. Under normal operating conditions, once a subscriber unit is registered or is communicatively coupled to the communication network via a specific BTS, the subscriber unit remains communicatively coupled to that BTS so long as the subscriber unit remains within that BTS communication site.
BTSs require routine maintenance procedures and periodic software code and configuration updates to ensure optimum operation of the wireless communication system. The performance of these procedures typically require that the BTS be removed from the communication network. In addition, the onset of unexpected malfunctions can cause degradation in BTS performance thereby affecting the BTS's ability to support communication functions and necessitating the transfer of subscriber units from the affected BTS to an alternate BTS at a neighboring communication site. Such malfunctioning BTSs are often removed from the communication network to perform trouble shooting procedures and implement corrective action.
One prior art method of removing a selected BTS from the communication network, involves the implementation of a communication protocol between the communication network and the subscriber units so that subscriber units communicatively coupled to a particular BTS can be forced to migrate to an alternate BTS. This prior art method requires the expensive process of reflashing and retooling existing subscriber units.
Current technologies do not provide a cost effective method or apparatus for gracefully removing an active BTS from a communication network by transferring subscriber units engaged in calls to an alternate BTS without an interruption in communication services. Typically calls are dropped without any advance notice. The subscriber is required to re-initiate a new call at a neighboring communication site via an alternate BTS. If a subscriber unit is in the process of receiving a data packet transmission via the affected BTS, the data transmission is typically interrupted. The subscriber is required to reinitiate a new call via an alternate BTS and request retransmission of the entire data packet transmission. In addition, new subscribers are not precluded from communicatively coupling to the communication network via the affected BTS.
Thus there is a need for a cost effective method and apparatus for removing a selected BTS from a wireless communication system that minimizes the impact on communication services provided to subscribers.